The present invention relates generally to liquid crystal light valves, and more particularly, to a bias drive circuit and noise reduction technique for use with such liquid crystal light valves.
Previously, liquid crystal light valves have had their bias nodes driven by a sine wave signal source having a frequency of about 2 kHz. A disadvantage of the sine wave signal source is that peak voltage values are approximately double the average absolute values of the voltage. The operation of the liquid crystal light valve depends upon the magnitude of the average value of bias drive voltage, and not the peak or RMS values. The liquid crystal light valves have been driven asynchronously relative to an external video source, which causes a "waterfall" effect of moving horizontal noise lines on a display screen wherein an output image is viewed. It is well known that noise in motion is much more noticeable by a viewer than stationary noise, and this has been a problem with conventional liquid crystal light valve image projectors.
Consequently, it would be an improvement in the art to have an image projector employing a bias drive circuit that does not employ a sine wave drive signal and wherein the projector does not produce moving horizontal noise lines in the projected image.